This invention relates to chemically resistant thermosetting resin having very low contents of volatile organic components. More particularly, this invention relates to improved unsaturated polyester resins, particularly unsaturated isophthalate polyester resin compositions, which are suitable components for products having low contents of ethylenically unsaturated reactive solvent-monomer. Thermosetting resins of the invention with reduced content of styrene monomer and the improved unsaturated polyesters have demonstrated excellent physical properties and retention of strength and hardness in corrosive environments.
A versatile family of thermosetting materials known as unsaturated polyester resins comprise low molecular weight polyester polymers derived from unsaturated dibasic acids and/or anhydrides dissolved in unsaturated vinyl monomers. While dominant uses of unsaturated polyester resins are in conjunction with glass fiber or carbon fiber reinforcement to form laminar composites, unsaturated polyester resins are also used in casting processes, which usually contain high loadings of fillers or mineral aggregate.
Properties of thermosetting materials formed by the step growth esterification of glycols and dibasic acids can be manipulated widely by the choice of coreactant raw materials. Reactivity fundamental to the majority of commercial resins is derived from maleic anhydride as the unsaturated component in the unsaturated polyester, and styrene as dilutent and coreactant monomer. Propylene glycol is the principal glycol used in most compositions, and ortho-phthalic anhydride is the principal dibasic acid incorporated to moderate the reactivity and performance of the final resins. Although phthalic resins find wide application in ambient fabrication processes, isophthalic resins are more widely used in products employing high temperature forming processes.
Substitution of isophthalic acid for phthalic anhydride provides enhanced mechanical and thermal performance and improved resistance to corrosive environments, which are significant properties for a variety of products including underground gasoline storage tanks and large diameter sewer and water pipe.
However, the melting point of the higher molecular weight isophthalic polymer is much higher than ortho-phthalic resins, and blending temperatures in styrene must be increased to avoid freezing the polymer out. Due to the high molecular weight and high viscosity of these isopolyester resins in styrene, larger amounts of styrene are necessary to control viscosity of the blend.
Increasingly stringent policies and regulations for protection of the environment have increased need for thermosetting materials, particularly unsaturated polyester resins, having very low contents of volatile organic components, that is, having very low VOCs (xe2x80x9cvolatile organic contentsxe2x80x9d). For example, unsaturated isopolyester resins are desired in laminar composites with glass fiber reinforcement to enhance thermal endurance as well as to produce stronger, more resilient cross-linked plastics that demonstrate improved resistance to chemical attack. Since unsaturated isopolyester resin often makes up a substantial part of the composition as a whole, resin having very low contents of volatile organic components is quite important to achieving very low VOC for the composition as a whole.
However, it has been difficult to achieve desired low VOC in cross-linked plastics employing unsaturated polyester resins, particularly in systems employing a combination of unsaturated isopolyester with styrene as dilutent and coreactant monomer. Removal of styrene from compositions containing isopolyester resins in attempting to achieve a low VOC generally is accompanied by significant drawbacks that include causing viscosity of the resin compositions to increase to a undesirable extent, and/or loss of required physical and corrosion resistant properties.
There is, therefore, a present need for thermosetting resin compositions having low contents of volatile organic components.
It is desirable that improved unsaturated polyester resins, particularly unsaturated isophthalate polyester resin, should be suitable components for products having low contents of ethylenically unsaturated reactive solvent-monomer. For example, unsaturated isopolyester resins, which are desired in laminar composites with glass fiber reinforcement to enhance thermal endurance, should, as well, produce stronger, more resilient cross-linked plastics that demonstrate improved resistance to chemical attack.
Advantageously, such improvements shall be combined in a thermosetting resin with reduced content of styrene monomer which improved composition can demonstrate excellent physical properties, retention of strength, and hardness in corrosive environments
This invention is directed to overcoming the problems set forth above in order to provide thermosetting resin having low contents of volatile organic components. It is desirable to have an unsaturated polyester resin, particularly unsaturated isophthalate polyester resin composition, which is a suitable component for thermosetting products having low contents of ethylenically unsaturated reactive solvent-monomer, yet has excellent physical properties and retention of strength and hardness in corrosive environments.
Preferably, thermosetting resins of this invention have a Brookfield viscosity of less than about 1500 cps at 25xc2x0 C., more preferably less than about 1200 cps, and most preferably less than about 1000 cps.
Aspects of this invention include chemically resistant thermosetting resins having low contents of volatile organic components comprising (i) a minor amount by weight of ethylenically unsaturated reactive solvent, (ii) a major amount by weight of unsaturated polyester.
Unsaturated polyester of the invention is produced by a process which comprises (a) condensing dihydric alcohol with at least one dicarboxylic acid and/or anhydride of dicarboxylic acid to form a polymer of esterification having an acid number in a range upward from about 5 mg KOH/g polymer, and (b) reacting the polymer of esterification with an amount of glycidyl methacrylate to form unsaturated polyester having an acid number in a range downward from about 15 mg KOH/g unsaturated polyester. Preferably, the unsaturated polyester has an acid number which is in a range from about 1 to about 15 mg KOH/g of unsaturated polyester, more preferably acid number is in a range from about 1 to about 10, and most preferably acid number of the unsaturated polyester is in a range from about 1 to about 5 mg KOH/g of unsaturated polyester.
Weight ratios of glycidyl methacrylate to the polymer of esterification generally are in a range downward from about 0.005 AN, i.e., the product of 0.005 and the acid number of the polymer of esterification. Preferably, the weight ratio of glycidyl methacrylate to the polymer of esterification is in a range of from about 0.001 AN to about 0.005 AN. More preferably, the weight ratio of glycidyl methacrylate to the polymer of esterification is in a range of from about 0.001 AN to about 0.004 AN, and most preferably, from about 0.001 AN to about 0.003 AN.
Preferably, the polymer of esterification is formed by a process which comprises initially condensing a dihydric alcohol containing from 2 to 10 carbon atoms and an aromatic dicarboxylic acid while distilling off water of condensation to form a melt of polymer having an acid number in a range from about 5 to about 15 mg KOH/g of polymer, and then condensing the polymer with unsaturated dicarboxylic acid and/or anhydride of unsaturated dicarboxylic acid and or anhydride while distilling off water of condensation to form the polymer of esterification having an acid number, AN, in a range upward from about 10 mg KOH/g polymer.
One aspect of this invention is a chemically resistant thermosetting resin, having low contents of volatile organic components comprising (i) about 35 to about 45 parts by weight of ethylenically unsaturated reactive solvent, and (ii) about 65 to about 55 parts by weight of an unsaturated polyester produced by a process which comprises (a) initially condensing dihydric alcohol containing from 2 to 10 carbon atoms and isophthalic acid while distilling off water of condensation to form a melt of polymer having an acid number in a range from about 5 to about 15 mg KOH/g polymer, then condensing the polymer and maleic anhydride while distilling off water of condensation to form a polymer of esterification having an acid number, AN, of at least 10, and (b) further reacting the polymer of esterification with an amount of glycidyl methacrylate such that the weight ratio of glycidyl methacrylate to condensation polymer is in a range of from about 0.001 AN to about 0.004 AN to form unsaturated isopolyester having an acid number in a range from about 1 to about 15 mg KOH/g of unsaturated polyester. Preferably, polymer of esterification has an acid number in a range from about 10 to about 30 mg KOH/g of polymer, and more preferably AN is in a range from about 15 to about 25.
Another aspect of the invention is a composite composition having resistance to chemical attack comprising: about 25 to about 500 parts by weight of fibrous reinforcement material and/or filler; about 35 to about 45 parts by weight of ethylenically unsaturated reactive solvent; and about 65 to about 55 parts by weight of an unsaturated polyester. Advantageously, the unsaturated polyester is produced by a process comprising: (1) initially condensing dihydric alcohol containing from 2 to 10 carbon atoms and isophthalic acid while distilling off water of condensation to form a melt of polymer having an acid number in a range from about 5 to about 15 mg KOH/g polymer, (2) then condensing the polymer and maleic anhydride while distilling off water of condensation to form a polymer of esterification having an acid number, AN, in a range from about 15 to about 25 mg KOH/g polymer, and (3) further reacting the polymer of esterification with an amount of glycidyl methacrylate such that the weight ratio of glycidyl methacrylate to condensation polymer is in a range of from about 0.001 AN to about 0.004 AN to form unsaturated isopolyester having an acid number in a range from about 1 to about 10 mg KOH/g unsaturated polyester invention.
For a more complete understanding of the present invention, reference should now be made to the embodiments illustrated in greater detail and described below by way of examples of the invention.
In the chemically resistant thermosetting resins of this invention the ethylenically unsaturated reactive solvent comprises any material that can copolymerize with the unsaturated polyester. The ethylenically unsaturated reactive solvent that copolymerize with the unsaturated polyesters of this invention include at least one member of the group consisting of styrene, vinyl toluene, t-butylstyrene, chlorostyrene, divinyl benzene, xcex1-methylstyrene, diacetone-acrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, methacrylate, methyl methacrylate, butyl methacrylate, and butyl acrylate.
Preferably, the ethylenically unsaturated reactive solvent comprises styrene or vinyl toluene, and the amount of the solvent-monomer is in a range of from 25 to 45 percent by weight of the resin. More preferably, the amount of ethylenically unsaturated reactive solvent is in a range of from 35 to 45 percent by weight of the resin.
Polyhydric alcohols that are useful in preparing the polyesters include diols, triols and higher functionality alcohols. Preferably, the dihydric alcohol is at least one member of the group consisting of ethylene glycol, propylene glycol, neopentyl glycol, 1,3-butane diol, 1,4-butane diol, diethylene glycol, dipropylene glycol, trimethylpentane diol, and trimethylene diol. More preferably, the dihydric alcohol is at least one member of the group consisting of ethylene glycol, propylene glycol, neopentyl glycol, 1,3-butane diol, 1,4-butane diol, diethylene glycol, dipropylene glycol, and trimethylpentane diol. Most preferably, the dihydric alcohol is at least one member of the group consisting of ethylene glycol, propylene glycol, neopentyl glycol. Propylene glycol offers good physical properties at low cost. Better weathering and improved resistance to alkaline chemicals can be achieved by using neopentyl glycol.
Polycarboxlyic acids that are useful in preparing the polyesters include dicarboxylic acids or anhydrides, dicarboxylic acid halides and dicarboxylic esters. Preferably, the aromatic dicarboxylic acid and/or anhydride is at least one member of the group consisting of orthophthalic acid, isophthalic acid, terephthalic acid and orthophthalic anhydride.
Suitable unsaturated polycarboxylic acids, and their corresponding anhydrides and acid halides that contain polymerizable carbon-to-carbon double bonds include maleic anhydride, maleic acid and fumaric acid. Preferably, the aromatic dicarboxylic acid is isophthalic acid and the unsaturated dicarboxylic anhydride is maleic anhydride, and more preferably the unsaturated polyester has an acid number in a range from downward from about 10 mg KOH/g of unsaturated polyester.
Isophthalic resins are manufactured by two-stage processing to facilitate the dissolution of the isophthalic acid. In the first stage, the glycol and isophthalic acid react at temperatures of 210xc2x0 C. under an inert atmosphere to produce a clear melt. High pressure processing (207 kPa (30 psi)) and esterification catalysts such as hydrated monobutyl tin oxide are also widely employed to reduce the cycle times of two-stage processing. Maleic anhydride is added in the second stage and the final resin completed at 240xc2x0 C. to control color and molecular weight development. Isophthalic resins intended for corrosion application are processed to the highest molecular weight as can meet viscosity requirements a given styrene content. Reaction cycle is about 24 hours.
The polyesterification reaction is normally carried out in stainless steel vessels ranging from 8,000-20,000 liters, heated and cooled through internal coils. Blade agitators revolving at 70-200 rpm are effective in stirring the low viscosity mobile reactants, which are maintained under an inert atmosphere of nitrogen or carbon dioxide during the reaction at temperatures up to 240xc2x0 C.
Weigh tanks or meters measure the liquid glycols into the reactor. Solids are usually added from 25-kg bags or 1000-kg supersacks. Silo and auger are used widely for isophthalic acid, whereas phthalic anhydride and maleic anhydride are metered in molten form. A packed condenser efficiently separates water from glycol. The glycol is refluxed back into the reactor and the remaining condensate is incinerated on-site using a thermal oxidizer. Once the polymer is formed, it is cooled to below 180xc2x0 C. and drained into a cooled blend tank containing styrene monomer under high agitation.
Glass-lined reactor systems are used occasionally for halogenated resins to prevent corrosion of the reactor components. Copper and brass fitting should be avoided due to the significant influence on resin cure characteristics.
Other glycols can be used to impart selective properties to these simple compositions. Ethylene glycol (EG) is used to a limited degree to reduce cost, whereas diethylene glycol (DEG) produces a more flexible polymer that can resist cracking when impacted. Neopentyl glycol (NPG) is used in most commercial products to improve uv and water resistance. Alkoxylated derivatives of bisphenol A (BPA) not only impart a high degree of resistance to strong acidic and alkaline environments, but also provide resistance to deformation and creep at elevated temperatures.
Long-chain aliphatic acids such as adipic acid are generally used to improve flexibility and enhance impact properties, demonstrating subtle improvements over resins modified with the ether glycols (diethylene glycol) and polyether glycols (polypropylene glycol).
In view of the features and advantages of the chemically resistant thermosetting resins having very low contents of volatile organic components in accordance with this invention, as compared to the known systems with reduced content of ethylenically unsaturated reactive solvent as previously used, the following examples are given. The following Examples will serve to illustrate certain specific embodiments of the herein-disclosed invention. These Examples should not, however, be construed as limiting the scope of the novel invention as there are many variations which may be made thereon without departing from the spirit of the disclosed invention, as those of skill in the art will recognize.